1. Field of the Invention
The present invention relates to a process for the separation of hydrogen and/or deuterium and tritium from an inert gas flow which is contaminated with hydrogen and/or deuterium and/or tritium, wherein the inert gas which is to be purified is conducted along the primary side of an exchange wall for hydrogen isotopes, as well as relating to an arrangement for the effectuation of the process in the cooling circuit of a gas-cooled nuclear reactor.
Hydrogen (H), and its isotope deuterium (D), and tritium (T), occur as impurities, for example, in the cooling gas circuits of gas-cooled nuclear reactors in which inert gases, especially helium, are utilized as cooling gases. Thus, for example, produced in the reactor core of a high-temperature reactor (HTR) having a capacity of 500 MW.sub.th is a tritium quantity of about 10.times.10.sup.3 Ci each year. The tritium is removed, in a known manner, in a gas purifying installation which is connected to the cooling gas circuit and which is passed through by a portion of the cooling gas so that in the cooling gas circuit there is produced an equilibrium partial pressure in the cooling gas circuit which consists of about 2 .mu.bar, and for hydrogen between 10.sup.2 to 10.sup.3 .mu.bar. Due to the excess of hydrogen in comparison with water and tritium in the cooling gas circuit, due to the isotope exchange in the cooling gas flow, tritium is essentially present as hydrogen-tritium molecules. The radioactive tritium in the cooling gas circuit is conducted with the cooling gas flow to the components of nuclear reactor, whose walls it can penetrate as a result of permeation. In order to avoid the thereby occasioned environmental contaminations, it is attempted to provide for the lowest possible tritium concentration in the cooling gas circuit.
2. Discussion of the Prior Art
It is known to reduce the equilibrium partial pressure for tritium, water and hydrogen through the purifying of a portion of the cooling gas flow. The branched off portion of the cooling gas flow is conveyed in a bypass conduit of the cooling gas circuit to a gas purifying installation. In the gas purifying installation, the water is quantitatively removed in the form of the H.sub.2 O, HDO or HTO, and the hydrogen in the form of H.sub.2, HD or HT. Thereby the cooling gas flow is conducted, for example, over a cooled copper oxide bed (CuO) so that hydrogen, deuterium and tritium are oxidized and condensed. In this purifying process it is disadvantageous that only a partial gas flow in the magnitude of several parts per thousand and less than the total cooling gas flow for each cooling gas flow cycle can be purified, and thereby a satisfyingly low partial pressure for tritium is not achieved in the cooling gas circuit.
A filter for the separation of tritium is known from U.S. Pat. No. 3,848,067, in which yttrium which evidences a high retention capacity for the hydrogen isotopes, is employed for hydrogen storage. For the separation of the hydrogen isotopes from the cooling gas circuit with yttrium, the cooling gas flow is conducted along the surface of the nickel-coated yttrium so that the hydrogen isotopes will permeate through the nickel coating and will be stored in the yttrium essentially in the form of metal hydrides. Subsequent to the enrichment of the hydrogen isotopes in the yttrium, the filter must be exchanged. It is disadvantageous that the filtering effect reduces with increasing hydrogen enrichment in the yttrium, and the filter, in accordance with partial pressure conditions of the hydrogens which are to be separated from the inert gas flow, can already become ineffective within a short time.